The performance of a lubricant degrades over time, which defines its specified oil drain interval. The degradation rate of a lubricant is dependent up the rate at which the activity of the additives contained in the lubricant degrades over time. Conventional ways in approaching this challenge is by developing or identifying additives that are more robust or more oxidatively stable so that they can persist longer in the lubricant environment, however this can often come at the cost of additive performance. Alternatively, lubricants formulations contain higher treat rates of the additives with the hopes of extending the performance of that additive to a longer lifetime. But this is often difficult as lubricant formulations are a delicate balance of additives and overtreating one additive can have significant negative impacts on the performance of another.
Time release additives for engine oils are known. These additives are typically incorporated into thermoplastic polymers which slowly dissolve into the engine oil. See, for example, U.S. Pat. No. 4,075,098. Time release additives have also been incorporated into polymers which are oil-permeable at elevated engine temperatures. See, for example, U.S. Pat. No. 4,066,559.
Replenishment of additives in a lubricant, by using a controlled release gel or other means to add additional additive to the lubricant, can improve the performance of the lubricant and the device using the lubricant. Use of controlled release gels, as described in U.S. Pat. No. 6,843,916, can replenish a lubricant with fresh additives over time. Such gels are formed by incorporating additive components which are compatible with the functional fluid to which the additive is to be delivered into a gel matrix. These gel matrixes often result from the interaction of a basic component and an acidic component, forming the gel.
There is a need for extending the life of current lubricant additives without compromising on additive performance and without increasing the initial treat rate of active additive. In addition, there is a need for improving the solubility of additives in lubricants, thereby reducing the need for co-base stocks (e.g., alkylated naphthalene such as AN5 or polar esters) or providing a mechanism to stabilize less soluble additives in lubricant formulations.